Lithium ion secondary batteries, which feature small size and large capacity, have been widely used as power supplies for electronic devices such as mobile phones and notebook computers and have contributed to enhancing convenience of mobile IT devices. In recent years, larger-scale applications, such as power supplies for driving motorcycles and automobiles and storage cells for smart grids, have attracted attention. As the demand for lithium ion secondary batteries has increased and they have been used in various fields, batteries have been required to have characteristics, such as further higher energy density, lifetime characteristics that can withstand long-term use, and usability under a wide range of temperature conditions.
Although carbon-based materials are usually used in a negative electrode of the lithium ion secondary battery, in order to increase the energy density of the battery, using a silicon-based material absorbing and desorbing a large amount of lithium ions per unit volume in the negative electrode is studied. However, there is a problem in that the silicon-based materials expand and contract by repeating charge and discharge of lithium, and thereby, the active material layer is damaged and peels off from the current collector to deteriorate the cycle characteristics of the battery.
It is known that a polyimide resin having higher mechanical strength is used as a binder in a negative electrode using the silicon-based material in order to solve this problem. Patent Document 1 discloses a reaction product between an aromatic diamine and an aromatic tetracarboxylic acid dianhydride as a specific example of the polyimide resin. Patent Document 2 discloses a polyimide resin consisting of a reaction product between an aromatic diamine and an aliphatic tetracarboxylic acid, which can improve charge and discharge efficiency compared with a polyimide resin consisting of a reaction product between an aromatic diamine and an aromatic tetracarboxylic acid anhydride. Patent Document 3 discloses a polyimide resin consisting of a reaction product between an alicyclic diamine and an aromatic tetracarboxylic acid.